1. Field of the Invention
The present invention relates to a working system, including a working robot, for practicing predetermined work, machining, welding, assembling or the like on moving subject works.
2. Description of Related Art
In the course of increasing automation in a manufacturing line used to produce mechanical products, it has proven to be necessary also to automate and simplify the application of predetermined work, such as the application of adhesives, to subject works. Much attention has been given to various approaches relating to techniques of accurately keeping a predetermined relative position between a working apparatus or device, such as an automatic adhesive application gun, and a subject work. Because of differences in dimensions among surfaces of subject works due to manufacturing errors and also because of differences in transported positions due to operational differences among conveyor systems, it is difficult to make proper adhesive application onto predetermined points or parts of subject works. Various efforts have been made to place an automatic adhesive application gun in an appropriate position relative to surfaces of subject works in order to provide for optimum utilization of the automatic working apparatus.
One such effort is that described in Japanese Utility Model Publication No. 3-40386. The approach used was to correct the position of an adhesive application gun according to results of measurement of target points at which adhesive is applied to a subject work.
While the automatic working apparatus as described in the above publication may have advantages over the prior art, nevertheless, subject works must be stopped during the application of adhesive. This is not always desirable.
In Japanese Utility Model Publication No. 1-35792, a welding apparatus is provided which does not stop the transportation of subject works while performing predetermined work. For the purpose of providing a brief description of the operation of the prior art working apparatus that will enhance an understanding of the present invention, reference is made to FIGS. 8 and 9.
Referring to FIGS. 8 and 9, a conveyor 51, only schematically shown, transports a subject work, such as a vehicle body 53 placed on a pallet 52, to a working apparatus 54. When a post 55 extending vertically from the pallet 52 is detected by means of a sensor 56, a control unit 57 puts out a signal S1 for causing a clamp arm 58 to hold the post 55 with hands 59 and 60. Then, a support device 61 placed on a working table 63 is coupled to the pallet 52 and slides on the working table 63 together with the pallet 52. When the support device 61 and pallet 52 move as one whole to a position where a work sensor 62 detects the head of the vehicle body 53, the control unit 57 provides a drive signal S2 for actuating a motor 64 and a lock signal S3 for causing a switch valve 65 to be locked. The motor 64 moves the working table 63 in synchronism with the conveyor 51. On the other hand, when the switch valve 65 is locked, the support device 61 is fixed to the working table 63. Consequently, thereafter, the working table 63 moves together with the vehicle body 53 placed on the pallet 52. Then, the control unit 57 provides for a working robot 66 a control unit S4 so as to practice predetermined work, such as welding, on a predetermined point of the vehicle body 53 installed on the working table 63. A distance between the work sensor 62 and a position where the working robot 66 performs the predetermined work is previously fixed so as to be equal to a distance between the body head and the predetermined welding point of the vehicle body 53. Consequently, based on a output signal from the work sensor 62, the control unit 57 causes the motor 64 to provide a controlled movement of the working table 63. It is intended to provide an appropriate relative position between the vehicle body 53 and the working robot 66 through this controlled movement and thereby enable the application of adhesive to subject works at accurate points.
In the prior art working apparatus, which practices predetermined work on moving subject works, the working robot 66 is moved at a synchronous speed with the conveyor 51 so as to maintain a predetermined relative position between the working robot 66 and the subject work 53. However, as a practical matter, it is difficult to maintain the subject work 53, transported by the conveyor 51, and the working robot 66, driven by the drive motor 64, stationary with respect to each other while they are united as one whole. This is because the subject work 53 and working robot 66 are each adversely affected by the transportation means for the other. In addition, if a load on the working robot 66 for driving the working table 53 is large, it is hard to provide a precisely synchronized movement of the working table 53 with the subject work 53 transported by the conveyor 51.